An energy-based fatigue life assessment model for various metallic materials under proportional and non-proportional loading conditions

The present study examines the capability of a lately developed energy-based fatigue damage parameter [Jahed H, Varvani-Farahani A. Upper and lower fatigue life limits model using energy-based fatigue properties. Int J Fatigue 2006;28:467–73] to assess fatigue life of various metallic materials subjected to proportional and non-proportional loading conditions. The proposed damage is defined based on (i) shear and axial stress and strain components responsible for cracking/modes of failure dominantly Case A and Case B, (ii) energy-based fatigue coefficients analogous to Coffin–Manson’s coefficients, (iii) corresponding fatigue lives of components failed under axial and torsional loading conditions, and (iv) total elastic–plastic energy calculated from stress–strain hysteresis loops. For the latter, the modified Mroz cyclic plasticity model has been employed to calculate the hysteresis energy. Using this model in conjunction with the proposed damage parameter, fatigue lives of different materials have been predicted and then compared with reported experimental data in the literature. The predicted fatigue lives based on the proposed damage model were found in very good agreement as compared with experimental fatigue data of various metallic materials of Al 7075-T6, AISI 304, SAE 1045, 1% Cr–Mo–V steel, Inc 718 and Haynes 188 tested under both proportional and non-proportional loading conditions.